The implementation of Blended Learning (BL) in teacher training, which demands learners to have high autonomy and complete tasks independently in an online environment, has established self-directed learning (SDL) a prerequisite for success. However, traditional SDL scales primarily focus on psychological attributes in face-to-face settings, often failing to capture the unique self-regulatory and technological dimensions required in a BL environment. While online readiness scales exist, they frequently treat SDL as a single dimension rather than a multidimensional competency essential for pre-service teachers. To address this gap, the study developed and validated a new SDL scale, specifically tailored to pre-service teachers in a BL context. Based on established theoretical frameworks (e.g. SDLI, AMS, and PRO), the study conducted a pilot survey (N=183) and a main survey (N=1,041) with pre-service teachers. The scale was validated through Cronbach’s Alpha, EFA (using SPSS), and a PLS-SEM model to ensure reliability, convergent validity, and discriminant validity. The results established an SDL scale consisting of 7 core factors, suitable for BL context. Furthermore, the model identified 4 key factors, explaining 67.4% of the variance in SDL. These factors include: Awareness (Student awareness), Community (Community interaction), Tech (Technology competence), and Year (School year). Notably, demographic variables such as Gender and Major were determined to have no statistically significant effect on SDL. These findings provide a valid assessment tool and a robust explanatory model, allowing educators and administrators to design effective pedagogical interventions, focusing on factors that can directly impact and improve core SDL competencies for the next generation of teachers.